In relation to a conventional art image forming apparatus such as a laser printer, a motor drive unit, which has a control circuit for effecting digital control and a motor drive circuit for driving a motor upon receipt of a command from this control circuit, for controlling a brushless DC motor is provided. For instance, JP-A-2000-134787 discloses an image forming apparatus having a main motor driver and a polygon motor driver, which are provided on separate control boards. The main motor driver drives and controls a main motor. The main motor performs mechanical driving of an image forming unit, a transfer unit, a fixing unit, and the like. The polygon motor driver drives and controls a polygon motor used for rotating a polygon mirror of a scanner unit that exposes the surface of a photosensitive drum in order to form an electrostatic latent image.